TYPO3 has a clean bootstrapping process driven mostly by class \TYPO3\CMS\Core\Core\Bootstrap. This class is initialized by calling Bootstrap::init() and serves as an entry point for later calling an application class, depending on several context-dependant constraints.

Each application class registers request handlers to run a certain request type (e.g. eID or TSFE-logic, or Ajax requests in the Backend). Each application is handed over the class loader provided by Composer.


There are four types of applications provided by the TYPO3 Core:


This class handles all incoming web requests coming through index.php in the public web directory. It handles all regular page (TSFE) and eID requests.

It checks if all configuration is set, otherwise redirects to the TYPO3 Install Tool.


This class handles all incoming web requests for any regular backend call inside typo3/*.

Its TYPO3\CMS\Backend\Http\RequestHandler is used for all backend requests, including Ajax routes. If a get/post parameter "route" is set, the backend routing is called by the RequestHandler and searches for a matching route inside the router. The corresponding controller / action is called then which returns the response.

The Application checks if all configuration is set, otherwise it redirects to the TYPO3 Install Tool.


This class is the entry point for the TYPO3 command line for console commands. In addition to registering all available commands, this also sets up a CLI user.


The install tool Application only runs with a very limited bootstrap set up. The failsafe package manager does not take the ext_localconf.php of installed extensions into account.

Example of bootstrapping the TYPO3 Backend:

// Set up the application for the backend
call_user_func(function () {
    $classLoader = require dirname(__DIR__) . '/vendor/autoload.php';
    \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::run(1, \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::REQUESTTYPE_BE);


Whenever a call to TYPO3 is made, the application goes through a bootstrapping process managed by a dedicated API. This process is also used in the frontend, but only the backend process is described here.

The following steps are performed during bootstrapping.

1. Initialize the class loader

This defines which autoloader to use.

2. Run SystemEnvironmentBuilder

The \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder is responsible for setting up a system environment that is shared by all contexts (FE, BE, Install Tool and CLI). This class defines a large number of constants and global variables. If you want to have an overview of these base values, it is worth taking a look into the following methods:

  • SystemEnvironmentBuilder::defineTypo3RequestTypes() defines the different constants for determining if the current request is a frontend, backend, CLI, Ajax or Install Tool request.
  • SystemEnvironmentBuilder::defineBaseConstants() defines constants containing values such as the current version number, blank character codes and error codes related to services.
  • SystemEnvironmentBuilder::initializeEnvironment() initializes the Environment class that points to various parts of the TYPO3 installation like the absolute path to the typo3 directory or the absolute path to the installation root.
  • SystemEnvironmentBuilder::calculateScriptPath() calculates the script path. This is the absolute path to the entry script. This can be something like '.../public/index.php' or '.../public/typo3/index.php' for web calls, or '.../bin/typo3' or similar for CLI calls.
  • SystemEnvironmentBuilder::initializeGlobalVariables() sets some global variables as empty arrays.
  • SystemEnvironmentBuilder::initializeGlobalTimeTrackingVariables() defines special variables which contain, for example, the current time or a simulated time as may be set using the Admin Panel.

3. Initialize bootstrap

\TYPO3\CMS\Core\Core\Bootstrap boots up TYPO3 and returns a container that is later used to run an application. As a basic overview it does the following:

  • Bootstrap::initializeClassLoader() processes all the information available to be able to determine where to load classes from, including class alias maps which are used to map legacy class names to new class names.
  • Bootstrap::checkIfEssentialConfigurationExists() checks if crucial configuration elements have been set. If that is not the case, the installation is deemed incomplete and the user is redirected to the Install Tool.
  • Bootstrap::createConfigurationManager() creates the Configuration Manager which is then populated with the the main configuration ("TYPO3_CONF_VARS").
  • $builder->createDependencyInjectionContainer() creates a dependency injection container which is later returned by Bootstrap::init().
  • The caching framework and the package management are set up.
  • All configuration items from extensions are loaded
  • The database connection is established

4. Dispatch

After all that the, the newly created container receives the application object and Application::run() method is called, which basically dispatches the request to the right handler.

5. Initialization of the TYPO3 backend

The backend request handler then calls the MiddlewareDispatcher which then manages and dispatches a PSR-15 middleware stack. In the backend context this will typically go through such important steps like:

  • checking backend access: Is it locked? Does it have proper SSL setup?
  • loading the full TCA
  • verifying and initializing the backend user

Application context

Each request, no matter if it runs from the command line or through HTTP, runs in a specific application context. TYPO3 provides exactly three built-in contexts:

  • Production (default) - should be used for a live site
  • Development - used for development
  • Testing - is only used internally when executing TYPO3 Core tests. It must not be used otherwise.

The context TYPO3 runs in is specified through the environment variable TYPO3_CONTEXT. It can be set on the command line:

# run the TYPO3 CLI commands in development context
TYPO3_CONTEXT=Development ./bin/typo3

or be part of the web server configuration:

# In your Apache configuration (either .htaccess or vhost)
# you can either set context to static value with:
SetEnv TYPO3_CONTEXT Development

# Or set context depending on current host header
# using mod_rewrite module
RewriteCond %{HTTP_HOST} ^dev\.example\.com$
RewriteRule .? - [E=TYPO3_CONTEXT:Development]

RewriteCond %{HTTP_HOST} ^staging\.example\.com$
RewriteRule .? - [E=TYPO3_CONTEXT:Production/Staging]

RewriteCond %{HTTP_HOST} ^www\.example\.com$
RewriteRule .? - [E=TYPO3_CONTEXT:Production]

# or using setenvif module
SetEnvIf Host "^dev\.example\.com$" TYPO3_CONTEXT=Development
SetEnvIf Host "^staging\.example\.com$" TYPO3_CONTEXT=Production/Staging
SetEnvIf Host "^www\.example\.com$" TYPO3_CONTEXT=Production
# In your Nginx configuration, you can pass the context as a fastcgi parameter
location ~ \.php$ {
   include         fastcgi_params;
   fastcgi_index   index.php;
   fastcgi_param   TYPO3_CONTEXT  Development/Dev;
   fastcgi_param   SCRIPT_FILENAME  $document_root$fastcgi_script_name;

Custom contexts

In certain situations, more specific contexts are desirable:

  • a staging system may run in a Production context, but requires a different set of credentials than the production server.
  • developers working on a project may need different application specific settings but prefer to maintain all configuration files in a common Git repository.

By defining custom contexts which inherit from one of the three base contexts, more specific configuration sets can be realized.

While it is not possible to add new "top-level" contexts at the same level like Production and Testing, you can create arbitrary sub-contexts, just by specifying them like <MainContext>/<SubContext>.

For a staging environment a custom context Production/Staging may provide the necessary settings while the Production/Live context is used on the live instance.

Usage example

The current Application Context is set very early in the bootstrap process and can be accessed through public API for example in the config/system/additional.php file to automatically set different configuration for different contexts.

In file config/system/additional.php:

switch (\TYPO3\CMS\Core\Core\Environment::getContext()) {
   case 'Development':
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 1;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '*';
   case 'Production/Staging':
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 0;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '192.168.1.*';
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 0;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '';